1. Field of the Invention
The present invention relates to novel precipitated silica particulates having a low water uptake, a process for the preparation thereof, and to the use of such precipitated silica particulates for the reinforcement of, e.g., silicone elastomers and silicone pastes.
2. Description of the Prior Art
It is known to this art to use the pyrogenic silica particulates as reinforcing fillers for vulcanizable organopolysiloxane compositions. However, the pyrogenic silicas suffer the disadvantage of being quite costly.
For many years, numerous attempts have been made to replace, at least in part, the pyrogenic silicas with the less expensive precipitation silicas. Various processes have been proposed to the art for the preparation of the precipitated silicas, complex processes, according to which such parameters as temperature, reagent concentrations, pH values, etc., need be carefully controlled (French Patent No. 1,352,354).
Attempts have also been made to improve the properties of precipitation silica for silicone applications by rendering the silica hydrophobic via appropriate surface treatments (using, for example, appropriate silane or silazane). Hydrophilic silicas made hydrophobic by such treatments and useful for silicone applications are described, for example, in French Patent No. 2,356,596. However, these treatments impart considerable cost to such processes.
An improved precipitated silica useful for the reinforcement of organopolysiloxane elastomers has been described (International Rubber Conference, Kiev, Oct. 10-14, 1978). Precipitation silicas of such type may have valuable properties, but are still inadequate relative to water uptake, this latter characteristic being essential for all silicone applications and in particular with regard to the dielectric properties of the final compositions, which are important in the more specialized applications, such as for the manufacture of cables.